In an electricity grid, demand response refers to managing the demand side (customer domain) in response to supply conditions, in particular in periods of peak demand. Load shedding is a type of demand response application to temporarily and on demand reduce the power consumption of electric appliances (i.e. loads). Typical examples are dimming of lights, decreasing setpoints of HVAC (heating, ventilation, and air conditioning), or using energy saving modes of consumer electronics equipment. Thus, load shedding is what electric utilities want their customers to do when there is a huge demand for electricity that exceeds the generation available.
Demand response can be realized simply via manual control of appliances, but centralized control (from a management station) has obvious advantages. For central control, communication between a central controller (e.g. building management station) and the appliances is required.
Demand response can be done in a “best effort” manner, but there may also be conditions requiring very precise reduction. Such conditions can be the contract between the demand response provider (the customer) and the receiver (e.g. a utility), or just the goal to limit the reduction to “what is required”, e.g. because the related decrease of user comfort (e.g. by dimming) shall be minimized. Precise consumption reduction can be achieved if exact operation status information of the appliances is available and/or the appliances can be individually controlled by the central controller hosting related programs to determine the required command parameters. This is, however, the ideal case. Many control systems lack at least parts of these fine-grained capabilities. Typical restrictions are unknown status of individual appliances, i.e., the complete system appears as “black box”, or no individual addressing of appliances, i.e. all appliances receive the same command.
Conventional solutions for such restricted systems include uniform shedding or stepwise shedding to pre-programmed levels (via a broadcast command) as described for lighting loads in the US2010/0117620A1, measuring the effect of the shed, i.e. the system consumption after the shed command, shed to the next level if consumption reduction is (still) insufficient, and when a consumption level below the target is reached, but it shall be closer to the target, the consumption level may be increased again, e.g. to a level halfway the last two sheds.
However, in a restricted system as described above, “overshooting” may occur when the system reduces the system power consumption more than required, which may lead to undesired effects (e.g. in case of dimming lights) where user comfort is more decreased than necessary. Moreover, a so-called “see-saw” effect may occur if target consumption is achieved by reduction and increase of consumption in one procedure, this may affect user comfort significantly (e.g. in case of dimming lights). In addition, “unfair distribution” may be faced. Looking at relative power levels (i.e. relative to the maximal consumption of an appliance), it is unfair to equally distribute the load change over all appliances. Loads that are already at a low consumption level will still have to shed further. In such cases, it may be desirable to first reduce the loads at high consumption levels.